A Mechanistic Study of the Cobalt(I)-Catalyzed Amination of Aryl Halides: Effects of Metal and Ligand.

Transition-metal-catalyzed amination of aryl halides is a useful approach for the synthesis of medicinal compounds, organic functional materials, and agrochemical compounds. A systematic DFT study has been performed to investigate the mechanism of the Co(I)-catalyzed amination of aryl halides by LiN(SiMe) using (PPh)CoCl as the precatalyst. Our computational results suggest that the most favorable dissociative concerted C-I activation pathway in a triplet state consists of (a) dissociation of one PPh ligand, (b) concerted oxidative addition (OA) of the C-I bond, (c) transmetalation, (d) (optional) dissociation of the second PPh ligand, (e) C-N bond-forming reductive elimination (RE), and (f) ligand exchange to regenerate the active species.

Petroleum spill bioremediation by an indigenous constructed bacterial consortium in marine environments.

In the process of marine oil spill remediation, adding highly efficient oil degrading microorganisms can effectively promote oil degradation. However, in practice, the effect is far less than expected due to the inadaptability of microorganisms to the environment and their disadvantage in the competition with indigenous bacteria for nutrients. In this article, four strains of oil degrading bacteria were isolated from seawater in Jiaozhou Bay, China, where a crude oil pipeline explosion occurred seven years ago.

Selective benzylic C-H bond activations mediated by a phosphorus-nitrogen PNP-nickel complex.

In contrast to the typical C-H activation, a PNP-Nickel complex chemoselectively cleaved the benzylic C-H bond of toluene in the presence of KHMDS, presumably an generated potassium benzyl intermediate. Under similar conditions, CO underwent deoxygenation to afford the corresponding nickel cyano complex, and ethylbenzene was dehydrogenated to give styrene and a nickel hydride compound. 2,6-Xylyl isocyanide was transformed into an unprecedented indolyl complex, likely by trapping the activated benzyl species with an isocyanide moiety.

Study on the Deterioration of Concrete under Dry-Wet Cycle and Sulfate Attack.

In order to study the deterioration and mechanism of dry-wet cycles and sulfate attack on the performance of concrete in seaside and saline areas, the deterioration of compressive strength of concrete with different water cement ratios under different erosion environments (sodium sulfate soaking at room temperature and coupling of dry-wet cycling and sodium sulfate) was studied here. At the same time, ICT (industrial computed tomography) and NMR (nuclear magnetic resonance) techniques were used to analyze the internal pore structure of concrete under different erosion environments. The results show that the compressive strength under different erosion environments increases first and then decreases, and the dry-wet cycle accelerates the sulfate erosion.

The Effects of Nano-SiO and Nano-TiO Addition on the Durability and Deterioration of Concrete Subject to Freezing and Thawing Cycles.

The objective of this manuscript is to study the effects of nano-particle addition on the durability and internal deterioration of concrete subject to freezing and thawing cycles (FTCs). Fifteen nm of SiO, 30 nm of SiO, and 30 nm of TiO were added to concrete to prepare specimens with different contents. All the specimens were subjected to FTCs from 0 to 75.

Interrogating the steric outcome during H heterolysis: in-plane steric effects in the regioselective protonation of the PNP-pincer ligand.

H heterolysis to generate well-defined nickel hydride-proton complexes was achieved by the 2 generation PNP-pincer nickel platform. The regioselective protonation in the ligand framework was demonstrated for the first time to highlight the importance of in-plane hindrance during the H splitting process.

A Missing Piece of the Mechanism in Metal-Catalyzed Hydrogenation: Co(-I)/Co(0)/Co(+I) Catalytic Cycle for Co(-I)-Catalyzed Hydrogenation.

Hydrogenation catalyzed by unusually low-valent Co(-I) and Fe(-I) catalysts were recently reported. In contrast to the classical M(I)/M(III) (M = Rh or Ir) or Ir(III)/Ir(V) catalytic cycles in the singlet state (adiabatic reactions) for Rh- or Ir-catalyzed hydrogenation, our systematic DFT study elucidates a new Co(-I)/Co(0)/Co(+I) catalytic cycle involving both singlet and triplet states (nonadiabatic reaction). Also, the more electron-rich cobalt center of the Co(-I) catalyst was found to contribute higher reactivity for alkene hydrogenation.

Nickel-catalyzed asymmetric hydrogenation of β-acylamino nitroolefins: an efficient approach to chiral amines.

An efficient approach for synthesizing chiral β-amino nitroalkanes has been developed the Ni-catalyzed asymmetric hydrogenation of challenging β-amino nitroolefins under mild conditions, affording the desired products in excellent yields and with high enantioselectivities. This protocol had good compatibility with the wide substrate scope and a range of functional groups. The synthesis of chiral β-amino nitroalkanes on a gram scale has also been achieved.

Reaction Mechanism of Cu(I)-Mediated Reductive CO Coupling for the Selective Formation of Oxalate: Cooperative CO Reduction To Give Mixed-Valence Cu(CO) and Nucleophilic-Like Attack.

A dinuclear, Cu(I)-catalyzed reductive CO coupling reaction was recently developed to selectively yield a metal-oxalate product through electrochemical means, instead of the usual formation of carbonate and CO ( Science 2010 , 327 , 313 ). To shed light on the mechanism of this important and unusual reductive coupling reaction, extensive and systematic density functional theory (DFT) calculations on several possible pathways and spin states were performed in which a realistic system up to 164 atoms was adopted. Our calculations support the observation that oxalate formation is energetically more favorable than the formation of carbonate and CO products in this cationic Cu(I) complex.

Metal-Free Synthesis of 3-Arylquinolin-2-ones from Acrylic Amides via a Highly Regioselective 1,2-Aryl Migration: An Experimental and Computational Study.

Combined experimental and theoretical investigations into the phenyliodine bis(trifluoroacetate) (PIFA)-mediated reaction of N-arylcinnamamide to produce 3-arylquinolin-2-one derivatives have been conducted. High regioselectivity during the aryl migration process was observed in 3,3-disubstituted acrylamides. Density functional theory calculation was conducted in an attempt to understand the mechanism and the origin of the regioselectivity.

A cascade amplification strategy based on rolling circle amplification and hydroxylamine amplified gold nanoparticles enables chemiluminescence detection of adenosine triphosphate.

A highly sensitive and selective chemiluminescent (CL) biosensor for adenosine triphosphate (ATP) was developed by taking advantage of the ATP-dependent enzymatic reaction (ATP-DER), the powerful signal amplification capability of rolling circle amplification (RCA), and hydroxylamine-amplified gold nanoparticles (Au NPs). The strategy relies on the ability of ATP, a cofactor of T4 DNA ligase, to trigger the ligation-RCA reaction. In the presence of ATP, the T4 DNA ligase catalyzes the ligation reaction between the two ends of the padlock probe, producing a closed circular DNA template that initiates the RCA reaction with phi29 DNA polymerase and dNTP.